Parallax measurements are widely employed to check the thickness of surface films, to measure the height of growth steps, to determine the plastic slip displacements, to determine the fractal dimensions of a fracture surface, and to estimate the roughness of ground and machined surfaces. In TEM and STEM techniques, the parallax measurements are also used to measure the thickness of the EM foil if a planar feature (see Figure 3772), such as a slip trace, precipitate, or stacking fault, whose crystallography is known, cuts the top and bottom surfaces of the foil. The thickness of the foil, t, can be given by,
θ -- The angle between the planar feature and the top and bottom surfaces of the foil
M -- The magnification
W -- The projected width, which is measured directly as shown in Figure 3772.
Figure 3772. Schematic illustration of the parallax measurements.